The alkyne group is a high-energy carbon-rich functionality that can serve as a perfect starting point for the preparation of conjugated molecules and materials. See Reference 1. For example, controlled cascade transformations featuring alkyne cyclizations provide practical means for the preparation of graphene nanoribbons. See References 1 through 4. On the other hand, alkenes, the reduced chemical cousins of alkynes, cannot serve as direct precursors for conjugated systems as alkenes cyclize to products that require an extra oxidizing step for aromatization.
Recently, we amplified the subtle chemical differences between alkenes and alkynes by utilizing dynamic covalent chemistry for the development of a regio- and chemoselective radical transformation of aromatic enynes into indenes. See References 5 and 6. Although both alkyne and alkene π-bonds are indiscriminately attacked by Bu3Sn radicals, the pool of four equilibrating isomeric radical intermediates is selectively depleted (“kinetically self-sorted”) through the “matched” 5-exo trig cyclization of the most reactive of the four radicals at the more reactive alkene π-bond.
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